Steam generating apparatus



Jan. 8, 1946. M. H. KUHNER 2,392,325

STEAM GENERATING APPARATUS Filed July 3, 1941 2 Sheets-Sheet 2 ooooooooI 3l oooooooo\ .2E 36 oooooooo oooooooo 33 MAX H. f1. UHNER FL-9. 6 f@Md. W

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Patented Jan. 8, 1946 STEAM GENERATING APPARATUS Max H. Kuhner,Worcester, Mass., assigner to Riley Stoker Corporation, Worcester,Mass., a corporation-of Massachusetts Application .my s, "194i, serial'No. 400,887

(ci. 12a-i.)

14 Claims.

This invention relates to the construction and operation of steamgenerating apparatus, and more particularly to apparatus of this typearranged to generate steam from the combustion products of two fuelshaving widely different characteristics, although in certain respectsthe invention is applicable where only a single fuel is utilized.

In many manufacturing plants low grade fuels are obtained as aby-product of the manufacturing procedure. For example, in steel millslarge quantities of blast furnace gas are produced, and in wood-workingplants considerable bark, sawdust, shavings and similar waste materialis available. It is desirable for economic reasons to utilize thesefuels for steam generation, but ordinarily they will not produce all thesteam which is required, and it is necessary to supplement them with ahigh grade fuel, such as pulverized coal or oil. 'I'his greatlycomplicates the problem of constructing the heat recovery equipment,including the economizer and air heater, through which the gaseousproducts of combustion travel after leaving the boiler heating surfaces.For a given rate of steam generation, the volume of the combustionproducts is very much greater with a low grade fuel than with a highgrade fuel. For example, the combustion products of blast furnace gasare approximately seventy percent greater in volume than the combustionproducts of pulverized coal for the same steam generating rate. If theheat recovery equipment is designed to permit operation at full loadwith pulverized coal, with a reasonable draft loss and reasonable powerrequirements for operation of the induced draft fan, it will be foundate at full load except during a small portion of the time. It shouldalso be noted in this connection that storage of blast furnace gas isnot practical, and it must be burned as fast as it becomes available, sothat there may be occasions when the ability to operate at very highloads with this fuel is of great importance. Further problems arise fromthe dimculties in maintaining ignition of the low grade fuel whenoperating at low combustion rates, and from the importance ofmaintaining the temperature of the gases in the heat recovery equipmentabove the dew point to avoid corrosion of the metal parts.

It is accordingly one object of the invention to provide a steamgenerating apparatus particurlarly adapted for use with fuels havingwidely different characteristics.

It is a further object of the invention to provide a steam generatingapparatus having heat recovery equipment of a size econbmicallyjustified for burning a combination of high and low grade fuels, and yetcapable of operating at full load with the low grade fuel alone withoutexcessive draft loss.

It is a further object of the invention to provide a new and highlyadvantageous combined arrangement of a steam boiler with an economizerand an air heater.

It is a further object of the invention to provide a steam boileradapted to be red with a combination of a high and a low grade fuel,together with heat recovery equipment so arranged as to make possibleoperation at high eiiiciency under normal conditions and yet allowoperation at full capacity with the low grade fuel, when required,without excessive draft loss.

With these and other objects in view, as will be L apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

Referring to the drawings illustrating one embodiment of the invention,and in which like reference numerals indicate like parts,

Fig. 1 is a longitudinal sectional view of steam generating apparatus,including certain heat recovery equipment;

Fig. 2 is a fragmentary elevation of the heat recovery equipment andcertain automatic control apparatus associated therewith; and

Figs. 3 to 6 inclusive are fragmentary sectional views showing certaindampers in different positions of adjustment.

The embodiment illustrated comprises a water tube steam boiler In ofwell-known construction having a furnace or combustion chamber Il and arear gas outlet l2. On the front wall of the furnace there is mounted aburner I4 suitable for a high grade fuel, such as pulverized coal, and asecond burner l5 suitable for a low grade fuel, such as blast furnacegas. Both burners are supplied with air for combustion purposes from aduct I6 which leads from an air heater I8 of a well-known type havingupright tubes I9. 'I'he air is delivered to the heater by means of aforced draft fan 20, and after flowing upwardly around the outersurfaces of the tubes I9 the heated air enters the duct I6. y

Above the air heater .there is located an economizer 22 of well-knownconstruction'having a series lof horizontal tubes 23. The boiler feedwater is supplied to the lower end of the economizer by an inlet pipe24, and after owing in a generally'upward direction through the tubes 23this water passes through a pipe 26 into the boiler I0.

'I'he upper end or gas inlet of the economizer is connected to theboiler gas outlet I2 by a passage 21, and the lower end or gas outlet ofthe economizer is connected to the upper end or gas inlet ofthe airheater I8 by'a passage 28. The lower end or gas outlet of the air heateris connected byan outlet passage 28 to an induced draft fan 8l.

With the construction as so far described the hot gaseous products ofcombustion will travel from the furnace Il through the boiler I0 to theoutlet I2, thence through the passage 21 and downwardly through theeconomizer 22, the passage 28, the tubes I9 of the air heater I8, andthe 'passage 2s to the induced draft fan, which wm discharge the gasesto a suitable stack (not shown). The temperature of the gases will bereducedby transfer of heat to the water in the boiler I0. to the feedwater in the economizer v tubes 23. and to'the airwhich surrounds thetubes I9 of the air heater I8. The flow of the gases through theeconomizer and air heater will be sexies flow, i. e. all the gases willtravel rst through the economizer and then through the air heater. Thisis well suited for highly efficient utinzation of the heat in the fue1.since the tem-` perature of the gases leaving the air heater will berelatively low. Furthermore, the economizer and the air heater will beso proportioned as to allow the boiler to be operated at full capacitywith such series flow, and without excessive draf-t loss, so .long aspulverized coal is used as the 3 of the economizer and air heater, sincethis would increase the cost and space requirements, all adding to thefixed charges on the installation.

These diiiiculties are avoided in accordance with .the present inventionby providing a construction such that when the draft loss through theeconomizer and air heater in series exceeds a predetermined amount,these apparatuses may be connected in parallel so that only a portion ofthe i gases will ow through each. This will reduce the draft loss, atsome sacrice of heat utilization, but

` with a considerable increase in the over-all efciency of theinstallation when all factors are considered. For .this purpose apassage 83 is provided leading froxn the boiler outlet I2 to the upperor inlet end of the air heater I 8, and a second passage 34 is providedleading from the lower or outlet end of the economizer 22 to the passage29.

l The passage 83 forms a by-pass for the economizer. and the passage 84forms a by-passfor the air heater. In order to control the ow of thegases in a desired manner a damper 86 is mounted in the passage 33, adamper 81 is mounted in the passage 34, and a damper 38 is mounted inthepassage 28. Because of the width of the last-mentioned passage, thedamper 88 is preferably of the double-vane type. The economizer by-pass88 connects with the passage 28 at a point posterior to the damper 88,whereas the air heater by-pass 84 connects with the 'passage 28 at apoint anterior to the damper 38. Consequently when .this damper isclosed. gases cannot flow from the by-pass 88 into the -by-pass 84.Preferably the by-passes 88 and 84 are connected to opposite sides ofthe passage 28, as this greatly simplifies the duct construction.

It will be apparent that with the dampers 86 and 81 both closed, asshown in Fig. 1, all the gas will be compelled to flow through theeconomizer A and air heater in series. If however, as shown in Fig. 4,the dampers 36 and 31 are open and the damper 88 closed, the economizerand air heater will be connected in parallel, each receiving a p0rtiononly of the gas, so that the draft loss will be comparatively low.

The severalv dampers are preferably so constructed and arranged thatthey may be controlled by automatic regulating mechanism during thenormal operation of the apparatus. For this purpose, as shown in Fig. 2,a regulator is connected to the damper 36a regulator 4I is connected tothe damper 31, and a regulator 42 is connected to the damper 38. Each ofthese regulators is of a'well-known type including a reversible motoroperated by compressed air, the construction being such that the motorwill assume predetermined positions dependent upon variations in thepressure of air or other iluid transmitted to the regulatorthroughaso-called impulse line." The regulators illustrated are of the typedisclosed in the patent to Donaldson No. 2,044,936, granted June 23, 1936. 'I'he two regulators 40 and 4I are connected to a single impulseline 44 leading from a master regulator 46 of the type disclosed in thepatent to Donaldson No. 2,177,823, granted October 31, 1939. This masterregulator is connected by a control pipe 46 to the passage 29 whichleads to the inlet of the induced draft fan 3l. These various parts areso constructed and arranged that so long as the suction in the passage29 remains below a predetermined value, say ten inches of water column,the pressure ln the impulse line 44 will be such -that the regulators 40and 4I will hold their respective dampers 86 and 31 closed. If howeverthe draft loss increases sufllciently to cause the suction inthe passage28 to exceed ten inches of water column, the master regulator will alterthe pressure in the impulse line 44 and cause the regulators 48 and 4Ito open .the dampers 36 and 81. Preferably the regulator 4I is adjustedto open its damper 81 slightly in advance of the damper 86, as indicatedin Fig. 3, the arrangement being such that if the suction in the passage28 continues to increase so that the damper 31 reaches its fully openposition, the damper 36 will then start to open.

The purpose of the damper 88 is to prevent reverse or upward flow of gasthrough the passage 28 when the dampers 36 and 81 are both open. If suchreverse ow could take place there would be no appreciable heat recoveryfromth gases leaving the boilers, since both the economizer and the airheater would be by-passed by the series connection of the passages 88,'2.8 and 84. In order to obtain the desired automatic control of thedamper 33, the regulator 42 is connected to an impulse line 48 leadingfrom a master regulator 43 'similar to the regulator 46. This regulator43 is connected to two control pipes 63 and 6I, these pipescommunicating with the passage 23 respectively anterior to and posteriorto the damper 33. Thus the regulator 43 is subjected to the pressuredrop or differential across the damper 33, and the parts are so adjustedas to maintain this drop at a predetermined small value, such asone-tenth inch of water column. Whenever this pressure drop becomes lessthan the established value, the damper 33 will be closed by itsregulator 42. Thus there can be no flow of gases from the passage 33into the passage 34 so long as the parts are under automatic control.

Under some circumstances it may be desirable for the operator to assumemanual control of the dampers. In order to make this possible, aseparate manual control station 63 is provided in the impulse line foreach of the regulators 43, l I, and 42. 'I'hese stations 53 are ofwell-known construction, and they make it possible for the operator toestablish, by a hand adjustment, a predetermined impulse pressure foreach damper regulator, so that each damper willbe held in acorresponding predetermined position.

IThe operation of the invention will now be apparent from the abovedisclosure. When starting up the steam generator from cold condition,the dampers 36, 31, and 33 will all be opened wide under manual control,as shown in Fig. 6. This will allow the [boiler gases to flowsuccessively through the passages 33, 28, and 34, by-passing theeconomizer and air heater. There will thus be no danger of steaming inthe economizer or condensation of water vapor in the air heater. Thisinitial warming up is preferably accomplished with pulverized coal,since blast furnace gas will not burn well without preheated air. Afterthe boiler has been brought up to its full working pressure, low loadoperation can be obtained with blast furnace gas by opening damper 36and closing dampers 31 and 33, as shown in Fig. 5. This will cause allthe combustion gases to flow through the passage 33 and the air heaterI3, affording the maximum preheat for the combustion air, and makingpossible stable combustion of the blast furnace gas. Under normal loadconditions the dampers will be controlled automatically, and so long asthe suction in the passage 23 remains below ten inches of water column,the dampers 36 and 31 will remain closed, as shown in Fig. 1. The gasflow will thus be in series through the economizer and air heater, withthe maximum recovery of heat. The damper 33 will be controlled by themaster regulator 43 and will close only enough to maintain a very slightpressure drop of one-tenth inch of water column across the damper. Ifnow the boiler load increases, or if more blast furnace gas is burned,the quantity of gases leaving the boiler outlet I2 will increase. Thiswill produce an increased draft loss through the boiler, the economizerand the air heater, so that the suction in the passage4 23 willincrease, causing a greater power requirement for operation of theinduced draft fan 3l. As soon as this suction reaches the predeterminedvalue of say ten inches of water column, the master regulator 45 willrespond thereto and alter the pressure in the impulse line M, causingthe regulator 4I to start to open the damper 31, as shown in Fig. 3.This will check the rise in the draft loss by causing part of the gasesto by-pass the air heater. At the same time the damper 33 will closestill further because of the decrease in the gas flow past the same. Ifthe draft loss continues to increase. the damper 31 will open fully, thedamper 36 will open, and the damper 33 will close, as shown in Fig. 4.This will connect the economizer and air heater in parallel, with partof the gases flowing through the economizer and the psage 34,whi1e theremaining gases ilow through the passage 33 and the air heater. Therewill be no flow through the passage 23. Because of the increasedflowarea available, the steam generator can be operated at high loads withblast furnace gas without excessive draft loss or excessive powerrequirements for the induced draft fan. As soon as the load on theboiler decreases suiilclently, or the quantity of blast furnace gasbeing burned decreases suillciently, the heat recovery equipment will berestored automatically to series operation.

' From the above disclosure it will be apparent that the invention makespossible highly efficient recovery oi the heat from the furnace gasesexcept on the very few occasions when unusually large amounts of blastfurnace gas must be burned, and yet even on such occasions there is noexcessive demand for power to drive the induced draft fan. Hence a motorof the usual size and construction may be employed. Furthermore theeconomizer and air heater can both be of normal size in proportion tothe steam generating capacity, and the fixed charges on the investmentwill therefore be moderate.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein. aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage connecting the economizer outlet tothe air heater inlet, a damper in the passage, an economizer by-passconnecting the boiler with the said passage posterior to the damper, anair heater by-pass connecting the said passage anterior to the damperwith the air heater outlet, and a separate damper in each by-pass.

2. Steam generating apparatus comprising a steam boiler, a fuelburningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet.and an outlet for gases, 'means to conduct gases from theboiler to the economizer inlet, a passage to conduct gases from theeconomizer outlet to the air heater inlet, a damper in the passage, aneconomizer by-pass connecting the boiler with the said passage posteriorto the damper, and an air heater by-pass connecting the said passageanterior to the damper with the air heater outlet.

3. Steam generating apparatus comprising a steam boiler. a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage to conduct gases from the economizeroutlet to the air heater inlet, a damper in the passage, an economizerby-pass connecting the boiler with one side of the said passageposterior to the damper, and an air heater 'by-pass connecting theopposite side of the said passage anterior to the damper with the airheater outlet.

4. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate.steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage to conduct gases from the economizeroutlet to the air heater inlet, an economizer by-pass connecting theboiler with the said passage, an air heater by-pass connecting the saidpassage with the air heater outlet, and means in the said passage toprevent flow of gases from the economizer by-pass to the air heaterby-pass. 5. Steam generating apparatus comprising a steam boiler, afuel-burning furnace associated therewith, the gaseous products ofcombustion from the furnace passing through the boiler to generate steamtherein, an economizer having an inlet and on outlet for gases, an airheater having an inlet and an outlet for gases, means to conduct gasesfrom the boiler to the economizer inlet, a fpassage to conduct gasesfrom the economizer outlet to the air heater inlet, an economizer bypassconnecting the boiler with one side of the said passage, an air heaterby-pass connecting the opposite side oi the said passage with the airheater outlet, and means in the said passage to prevent flow of gasesfrom the economizer bypass to the air heater by-pass.

6. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer and an air heater arranged to receive gases from the boiler,and automatically operable means responsive to variations in the volumeof gases and arranged to direct the gases through the economizer and airheater in series when the volume of the gases, is not excessive and inparallel when the volume of the gases is excessive.

7. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage connecting the economizer outlet tothe air heater inlet, a damper in the passage, an automatic regulatorarranged to control the damper in accordance with the drop in gaspressure across the damper and to maintain said drop at a smallpredetermined value, an economizer by-pass connecting the boiler withthe air heater inlet, an air heater by-pass connecting the economizeroutlet with the air heater outlet, and a separatedamper in each by-pass.

8. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage connecting the economizer outlet tothe air heater inlet, means to prevent reversal of the gas flow in thepassage, an induced draft fan, a, passage connecting the airheateroutlet to the fan, an economizer by-pass connecting the boilerwith the air heater inlet, an air heater by-pass connecting theeconomizer outlet with the air heater outlet passage, a separate damperin each by-pass. and automatic control mechanism arranged to open theby-pass dampers when required to prevent overloading of the induceddraft fan.

9. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and an outlet for gases, an air heater havingan inlet and an outlet for gases, means to conduct gases from the boilerto the economizer inlet, a passage connecting the economizer outlet tothe air heater inlet, means to prevent reversal of the gas flow in thepassage, an induced draft fan, a passage connecting the air heateroutlet to the fan, an economizer by-pass connecting the boilerl with theair heater inlet, an air heater by-pass connecting the economizer outletwith the air heater outlet passage, a separate damper in each by-pass,and automatic control mechanism arranged to open the by-pass damperswhen the suction in the air heater outlet passage exceeds apredetermined value.

10. Steam generating apparatus comprising a steam boiler, a fuel-burningfurnace associated therewith, the gaseous products of combustion fromthe furnace passing through the boiler to generate steam therein, aneconomizer having an inlet and a-n outlet for gases, an air heaterhaving an inlet and an outlet for gases, means to conduct gases from theboiler to the economizer inlet, a passage connecting the economizeroutlet to the air heater inlet, a damper in the passage, an automaticregulator arranged to control the damper in accordance with the drop ingas pressure across the damper and to maintain said drop at a smallpredetermined value, an induced draft fan, a passage connecting the airheater outlet to the fa-n, an economizer by-pass connecting the boilerwith the air heater inlet, an air heater by-pass connecting theeconomizer outlet with the air heater outlet passage, a separate damperin each by-pass, and automatic control mechanism arranged to open rstthe air-heater by-pass damper and then the economizer by-pass damperwhen the suction in the air heater outlet passage exceeds apredetermined value.

11. In a fluid heating unit having a pair of heat exchangers arranged toreceive heating gases generated therein, the method of burning two fuelsof different caloriflc values which comprises burning the higher caloricfuel therein and passing the heating gases generated through both ofsaid heat exchangers in series, and at other times burning the lowercalorific fuel therein and passing the heating gases generated throughboth of said heat exchangers in parallel,

12. In a steam generating unit having an economizer and an air heaterconnected to its gas outlet, the method of burning two fuels ofdifferent caloric values which comprises burning the higher calorificfuel and directing the gaseous products of combustion leaving the gasoutlet through the economizer and the air heater in series, andat othertimes burning the lower caloriflc fuel and directing the products ofcombusassasas tion leaving the gas outlet through the economizer and airheater in parallel.

13. In a vapor generating unit having a vapor generating section and apair of heat exchangers arranged to receive heating gases produced bythe combustion of fuels in an associated furnace chamber, the method ofburning fuels of substantially different calorii'lc values in saidfurnace chamber and directing said heating gases into heat transfercontact with said vapor generating section and thereafter into heattransfer contact with said heat exchangers without exceeding apredetermined draft loss throughout the operating range which comprisesburning said fuels in said chamber at substantially different volumetricrates of production of said heating gases, directing said heating gasesat low volumetric rates of production Athrough said heat exchangers inseries, and directing said heating gases at high volumetric rates ofproduction through said heat exchangers in parallel without varying theamount of heat exchanger surface contacted by said heating gases.

14. A fluid heater unit comprising a furnace chamber, a vapor generatingsectionarranged to receive heating gases produced in said furnacechamber, a pair of heat exchangers arranged to receive said heatinggases from said vapor generating section, means for burning fuel ofrelatively high caloriflc value in said furnace chamber and therebyproducing heating gases at a relatively low weight rate for a given rateof vapor generation, separate means for burning fuel of relatively lowcaloric value in said furnace chamber and thereby producing heatinggases at a relatively high weight rate for the same rate of vaporgeneration, and damper controlled conduit means associated with saidpair of heat exchangers and operable for passing said heating gases atlow weight rates of production through said pair of heat exchangers inseries and at high weight rates of production through said pair of heatexchangers in parallel comprising a substantially unobstructed heatinggas conduit opening to one end of one of said heat exchangers, a secondheating gas conduit opening to a space connecting adjacent ends of saidfirst and second heat exchangers, a control damper in said secondconduit, and damper means between said heat exchangers arranged in oneoperating position to provide a heating gas flow path through said pairof heat exchangers in series from said first heating gas conduit, and ina second operating position to provide a heating gas flow path throughsaid pair of heat exchangers in parallel.

MAX H. KUHNER.

